The present invention relates to a developing apparatus for depositing developer particles onto a latent image formed on an image carrier so as to obtain a visible image.
Conventional developers used in a developing apparatus of this type include one-component developers and two-component developers. A two-component developer consists of a toner contributing to development and a carrier for properly charging this toner. However, in such a two-component developer, a mixing ratio of the toner to the carrier must be kept constant. In other words, the toner concentration must be kept constant. However, it is difficult to maintain a constant toner concentration. On the other hand, a one-component developer has an advantage in that the concentration can be easily controlled since only the toner for contributing to development is contained in the developer.
One-component developers are classified into magnetic and nonmagnetic developers. Magnetic developers contain magnetic particles in the nonmagnetic developer particles. When such a magnetic developer is used in accordance with a conventional method, a magnet is arranged on a developer carrier for carrying the developer into the developing position so that the magnet generates a magnetic field for supporting the developer on the developer carrier. The following problems occur when the magnetic developer is used.
(1) The developer carrier becomes complicated, has a high cost and is large in size since the magnet must be supported by the developer carrier.
(2) The magnetic developer containing magnetic particles is more expensive than a nonmagnetic developer.
(3) Since the magnetic developer contains magnetic particles which do not contribute to development, color reproducibility is not very good. As a result, it is difficult to perform color development by pressing the magnetic developer.
To eliminate these drawbacks, a developing apparatus which uses a nonmagnetic developer has been proposed. When a nonmagnetic developer is used, it must form a thin layer on the developer carrier. If a thick layer is formed, it is liable to have a nonuniform thickness. Further, in this case, the developer particles may be electrically charged to different degrees. Consequently, a good image cannot be obtained.
In a conventional developing apparatus using a one-component nonmagnetic developer, a blade (press member) is arranged to apply the developer to the developer carrier so as to charge the developer by friction. However, since this blade is arranged only to charge the developer, the blade is firmly fixed on the developing apparatus by screws.
In order to form a thin uniform film of developer on the developer carrier, the pressure of the blade (press member) with respect to the developer carrier must be set at a predetermined value. However, in the conventional construction, the blade is firmly fixed by screws or the like on the developing apparatus, and the pressure of the blade with respect to the developer carrier cannot be adjusted. Moreover, the conventional apparatus which does not have adjusting mechanism is difficult to readjust the pressure, and thus is unusable.